The present invention relates generally to a rolling suspension system. More particularly, the present invention concerns an improved wheelchair having canted wheel rolling supports.
Conventionally, suspension systems for vehicular support utilize generally circular wheels mounted on horizontal axes for rotation. These wheels typically require a fairly hard surface to support them if the vehicle carried thereby is to be easily moved. In part, this is the cause for the cement, concrete and asphalt concrete highway systems existing throughout the world.
When conventional vehicle suspension systems do not operate on a fairly hard surface, much of the energy exerted in attempting to move the associated vehicle is wasted in depressing the comparatively soft surface to make way for the rolling supports. Construction vehicles and some military equipment partially overcome this difficulty by employing fairly wide articulated treads on which more conventional rolling wheels operate to support the vehicle.
Over the years, some variety has developed in these conventional vehicular support systems. For example, there exists a vehicle using inclined elliptical wheels that present a circular elevation. These vehicles track a sinusoidal path and are useful on soft terrain, See U.S. Pat. No. 3,363,713 issued Jan. 16, 1968 to J. E. Blonsky, and U.S. Pat. No. 2,683,495 issued July 13, 1954 to J. F. Kopczynski. Both these devices include differential gearing systems to aid negotiation of curved paths.
Vehicular supports with wheels tiltable about a transverse axis and rotatable about a fixed inclined axis are also known, See U.S. Pat. No. 3,001,601 issued Sept. 26, 1961 to Aghnides and U.S. Pat. No. 912,010 issued Feb. 9, 1909 to Martin.
Other varied forms of rolling geometry have been used in castors. Even inclined support surfaces have been applied in a variety of such devices. See for example U.S. Pat. No. 2,539,108 issued Jan. 23, 1951 to Shepherd; U.S. Pat. No. 3,161,907 issued Dec. 22, 1964 to Anthony; and U.S. Pat. No. 3,928,888 issued Dec. 30, 1975 to Lapham.
While generalized rolling supports are used in a variety of vehicles, the supports heretofore used on wheelchairs for disabled persons have been comparatively limited. In fact, wheelchair design has not undergone a significant revolution at any time in recent history.
A typical wheelchair now in widespread use employs a pair of fairly large diameter wheels mounted on a horizontal axle slightly behind the wheelchair occupant and a pair of casters mounted at the forward end of the wheelchair in order to stabilize it. This particular type of a wheelchair has numerous deficiencies from the standpoint of a disabled occupant required to use the wheelchair. For example, the occupant get very little useful exercise during propulsion of the wheelchair himself. As a result, muscles may atrophy from lack of use. In addition, the occupant cannot move his body weight relative to the chair in a manner to significantly change those portions of his body which support his weight. In such circumstances, it is difficult to maintain adequate blood circulation. This relative immobility can lead to painful adhesions in a post operative situation and other impairments because the human body works efficiently only in a dynamic environment. Still further, the wheelchair design is not readily adaptable for use with conventional furniture designed for use by nondisabled adults: for example, wheelchair seat height commonly exceeds the height of chairs ordinarily used with tables; and, wheelchair occupants cannot easily move themselves without assistance laterally to and from conventional chairs, beds, and the like.
While the foregoing discussion in itself demonstrates the need for an improved wheelchair, there are additional factors common to conventional wheelchair designs which are disadvantageous and undesirable with regard to operation. While this discussion is not intended to be exhaustive, some of the other problems associated with wheelchairs now available should be at least briefly mentioned.
For example, most wheelchairs are unstable when ascending an inclined surface. This instability requires an attendant to assist the wheelchair occupant in ascending such inclines. The cause of instability may generally be attributed to the fact that the center of gravity of the wheelchair and its occupant is above the effective center of rotation of the largest support wheel. With such a physical arrangement, coupled with the fact that the combined center of gravity of the occupant and the chair typically is positioned only slightly forward of the rear axle, an overturning force moment is permitted to exist when an unattended wheelchair attempt to ascend an inclined surface. But this axle location is necessary to permit the occupant to move the chair himself by grasping the large rear wheels.
Another aspect of conventional designs is that they are typically difficult for the occupant to propel by himself. More specifically, there is usually a circular rim laterally attached to large rear wheels which are intermittently operated by the occupant: the rim is manually gripped by the occupant, moved forward, and then released in order to propel the chair. This arrangement is objectionable not only since the chair can only be advanced at a rate at which the occupant can comfortably maintain but also because the disabled person must have coordinated use of both arms in order to effect locomotion of the chair. Moreover, the occupant wastes much energy in the intermittent operation.
Curbs and similar vertical barriers also present substantial obstacles to the known wheelchair designs. Because the wheels are circular and small enough to be manipulated by the seated occupant, it requires great effort to lift the wheelchair up a vertical obstruction. The existence of common vertical obstacles has, in recent times, been a partial impetus for placement of ramps at all curb intersections in municipal areas.
Maneuverability of existing wheelchairs is also a problem. For example, when entering closets, bathrooms, and similar confined areas, disabled persons confined to wheelchairs experience difficulty in manuevering their wheelchairs. Part of this difficulty stems from the inability of most devices to turn about a vertical axis which is occasionally required in these difficult close-quartered situations.
Most wheelchairs employ a pair of wheels of equal diameter. It is therefore difficult to maneuver those chairs along a gradually curving path since the wheels must rotate at slightly different peripheral speeds during negotiation of a long gradual curve. This is a problem experienced in automobiles and solved there by the use of a differential gearing system in the transmission. The known wheelchair assemblies do not exhibit such flexibility in their design.
While collapsible wheelchairs are, of course, widely used by disabled persons, the collapse movement is lateral to the conventional direction of movement of the chair. This lateral collapse associated with rigidity against forward/rearward chair articulation is unnatural. Thus, these wheelchairs constrain a disabled occupant in an unnatural manner since the major joints of a disabled person typically flex about axes perpendicular to the sagital plane. Accordingly, the lateral collapsibility of existing chairs is not amenable to permitting an adjustable seat having a plurality of positions which can be assumed by the disabled occupant.
For those wheelchair designs which do not rigidly establish the chair attitude, the design typically is not coordinated with the anatomy of the disabled occupant. One aspect of this lack of coordination concerns the potentially nauseating effect of motion on the disabled occupant. Commonly referred to as motion sickness, the nausea primarily results from oscillations of the head in a rocking motion about the horizon. Those wheelchair devices now available do not compensate for this problem.
Conventional wheelchairs also require two healthy arms for manual operation by the occupant. In many instances this requirement cannot be satisfied. Accordingly, the occupant needs the services of an attendant on almost a continual basis. Or, a special split hub contraption may be added which is expensive and interferes with the ability to collapse the chair to allow him to impart propulsion movements to either or both wheels with one hand.
In fact, conventional wheelchairs basically suffer from a common problem when a disabled person attempts to use one to lead an active life: the designs have evolved primarily for the institutionalized care of disabled persons. A preferred design would use a view toward helping disabled persons overcome the disability, maintain physical vitality, and obtain a maximum of personal mobility.
In view of the multifaceted discussion presented above, it will now be apparent to those skilled in the art that the need continues to exist for a rolling suspension system and, in particular, a wheelchair which overcomes problems of the type discussed.